The present invention relates to a brake fluid pressure control apparatus for a vehicle, and more particularly to a brake fluid pressure control apparatus for a vehicle, which is capable of increasing brake fluid pressure applied to wheel brakes through a pump.
In recent years, there has been proposed a brake fluid pressure control apparatus for a vehicle including an electric pump for supplying pressurized brake fluid to wheel brakes so that a braking force is proactively and automatically generated without requiring a brake pedal operation of the driver. Such a brake fluid pressure control apparatus generates a braking force to realize a collision mitigation brake system or a vehicle stability assist system.
For example, Japanese Laid-open Patent publication No. 2000-203401 discloses a brake control apparatus for a vehicle in which pumps and pressure regulating valves (shut-off valves) are used for controlling fluid pressure in wheel brakes. The pressure regulating valves are of a linear solenoid-type valve which can restrict flows of brake fluid from wheel brakes to the master cylinder with a pressure (valve closing force) according to an electric current applied to the valve.
However, in the case of the collision mitigation brake system where the target fluid pressure is gently increased at a slight inclination, the initial valve closing force of the pressure regulating valve is weaker when compared with the discharge pressure of the pump if an electric current in accordance with the target fluid pressure is applied to the pressure regulating valve. This is because the valve closing force of the pressure regulating valve increases gradually as with the target fluid pressure, and a weak valve closing force will be provided at an initial stage of the increase in the fluid pressure. This will cause a slight amount of brake fluid to flow through the pressure regulating valve toward the master cylinder, and hence the efficiency of increase in fluid pressure deteriorates accordingly.
In view of the foregoing drawback, the present invention seeks to provide a brake fluid pressure control apparatus for a vehicle, which is capable of quickly pressurizing fluid in a fluid pressure passage between the pressure regulating valve and the wheel brake so that the actual fluid pressure at the wheel brake comes closer to the target fluid pressure.